In recent years, idle-stop vehicles have been commercialized to reduce the amount of fuel consumption and exhaust gas. Idle-stop vehicles automatically stop (idle-stop) an engine upon detection of a halt operation of a vehicle due to a wait at a traffic light, or the like, and automatically restart the engine upon detection of a start operation of the vehicle.
In such idle-stop vehicles, a high electric current flows into a starter motor for starting an engine at the engine restart after being idle-stopped. Therefore, the voltage of a battery temporarily decreases. In association with this, a voltage output to a load such as an electronic device or the like other than the starter motor, connected to the battery, temporarily decreases. Accordingly, depending on a load, an input voltage deviates from a range of a voltage needed for operations, leading to the possibility of temporarily improper operations. There is also a possibility that an unintentional operation of a driver, such as a resetting of a car navigation system or an audio system, or jumpiness in an audio system, can occur.
Therefore, such idle-stop vehicles are provided with a power supply device between a battery and a load so that an output of a needed voltage to a load can be maintained even if the voltage of the battery temporarily decreases.
For example, an existing power supply device is presented such that the voltage of a battery is boosted and output to a load by continuously turning off a bypass switch and by operating a boost circuit at an engine restart after being idle-stopped, and the voltage of the battery is output to the load via the bypass switch by continuously turning on the bypass switch and by halting the boost circuit at normal times other than the engine restart. For example, see Patent Document 1.
Thus, the output of the needed voltage to the load can be maintained even if the voltage of the battery temporarily decreases in association with the engine restart after being idle-stopped. Moreover, the voltage of the battery is output to the load without being dropped by an element within a boost circuit at normal times other than the engine restart after being idle-stopped. As a result, the output of the needed voltage to the load can be maintained.